1. Field of the Invention
The present invention relates to an array refracting element and an exposure device, and specifically relates to an array refracting element used for changing resolution in an exposure recording apparatus, which scans a recording medium with light beams emitted from a light source so as to form an image, and to an exposure device in which resolution can be changed.
2. Description of the Related Art
Conventionally, an exposure recording apparatus has been used, wherein a drum, around which a photosensitive material (recording medium) is mounted, is rotated in a main-scanning direction, and laser beams, which have been modulated based on image data of an image to be recorded on the photosensitive material, are emitted in a sub-scanning direction orthogonal to the main-scanning direction, so as to record a two-dimensional image on the photosensitive material.
In order to record an image with a lower resolution in such an exposure recording apparatus, one of the following two methods has been used: method (1) in which a spot diameter of the laser beams on a surface of the photosensitive material is increased and a recording pitch in the sub-scanning direction is increased; and method (2) in which pixels comprising the same image data are repeatedly recorded based on the lowered resolution without increasing the spot diameter and the recording pitch. In order to record an image with a higher resolution, a method contrary to these methods has been used.
When the spot diameter of the laser beams is increased or decreased in this manner, however, a lens or the like serving as an optical system needs to be driven by using a driving mechanism, and thus, there has been a problem in that the apparatus is enlarged and cost is thereby increased. Further, when, in order to lower the resolution of the image, the pixels comprising the same image data are repeatedly recorded based on the lowered resolution, there has been another problem in that a recording speed cannot be improved because the recording pitch in the sub-scanning direction is fixed.
For the purpose of solving these problems, a technique described in Japanese Patent Application Laid-Open (JP-A) No. 2000-284206 was invented (an applicant thereof is the same as that of the present invention). A recording apparatus using this technique is provided with a plural condensing-points generation means, which divides a light beam emitted from a light source into plural light beams and generates plural condensing points on a recording medium in a sub-scanning direction thereof via a condensing optical system, and with a sub-scanning control means, which controls a recording interval in the sub-scanning direction based on a resolution. When the light beams emitted from the light source are condensed onto the recording medium via the condensing optical system so as to record an image, the number of the condensing points generated divisionally in the sub-scanning direction by the plural condensing-points generation means is controlled based on a resolution of the recording image, so as to adjust size of a beam spot and the recording interval between the beam spots in the sub-scanning direction, whereby the image can be efficiently recorded based on the resolution.
Further, in the recording apparatus using the above technique, a polarizing optical element formed by uniaxial crystal or a deviating prism is used as the plural condensing-points generation means.
However, when the polarizing optical element formed by uniaxial crystal is used as the plural condensing-points generation means in the recording apparatus using the technique described in JP-A No. 2000-284206, there has been a problem in that the uniaxial crystal is expensive and the entire cost of the apparatus is thereby increased.
Further, when the deviating prism is used as the plural condensing-points generation means in the recording apparatus using the technique described in JP-A No. 2000-284206, there has been another problem in that quality of the recording image may be degraded.
Specifically, when the deviating prism is used as the plural condensing-points generation means in the recording apparatus using the technique described in JP-A No. 2000-284206, as exemplified in FIG. 12, blur of the laser beams at positions in front of and behind a focal position (i.e., nearer to and farther away from the deviating prism with respect to the focal position) of the laser beams in a direction of the optical axis (depth direction), wherein the laser beams have been divided by the deviating prism and condensed by a condenser lens, are asymmetrical to each other in the direction of the optical axis.
Since the light beams divided by the deviating prism are respectively condensed by the condenser lens to different positions in a division direction at the focal position, the divided light beams incoming to the focal position separate from each other, and the divided light beams outgoing from the focal position approach each other, intersect and separate from each other. This results in the above-described asymmetrical phenomenon. This phenomenon reduces a range in which the recording medium can be disposed in the depth direction. Therefore, even when the position where the recording medium is disposed is slightly deviated in the depth direction, quality of the image recorded on the recording medium may be degraded.